Such an abrading tool can be produced according to a first conventional method wherein non-woven fibrous webs die-cut to form so called "disks" having a central hole are stacked one on another with a rotation driving shaft with a threaded free end disposed in the disk holes and then are compacted. The compacted disk webs are then held by two holding disk plates or bases having bores with a pair of key grooves through which the shaft extends with the shaft free end screwed into a nut. This method is disadvantageous in that the rotation driving shafts per se are required to produce such compacted multi-layer disk brushes in a first factory, and thus they are obliged to be transported from and returned to a second factory or user where the disk brushes are used with the driving shafts for abrading purposes. Further, for the second user, it is troublesome to disassemble the spindle from an abrading apparatus for sending the spindle to the first factory producing abrading brushes.
To avoid such transportation of the driving shafts, there are second and third known methods. According to the second method, a hollow cylindrical core of a resin, preferably, a paper sheet impregnated with phenol resin, is disposed in and tight-fitted with the central holes of the stacked abrasive webs with its opposite free end portions extending outwards of the stacked webs, and is fixed to the webs with an adhesive added between the core and the webs in the web holes. Each free end portion of the core is notched from the end edge thereof to form a pair of key grooves. During the above operation, a pair of plastic ring plates, so called "end plates" of, for example, PVC are mounted on the opposite end portions of the core to abut against the piled webs with the core end portions being inserted in the ring plates, respectively. Then, similarly, a cylindrical stopper ring of stainless steel notched from the end edge thereof to form a pair of key grooves for the below-mentioned flange is mounted on each core end portion so that its key grooves are aligned with the key grooves of the core and it abuts against the ring plate, and is fixed to the core with the adhesive. A pair of flanges serve as tools for mounting the grinding tool completed by the above operations on the spindle. Each flange has a cylindrical extension with a pair of key projections or reverse keyways for both the core and stopper ring and a central through-hole with a pair of key grooves therein for the spindle. The flanges are disposed in the core from the opposite core end portions to abut against both the core and stopper ring with the key projections being engaged with the aligned key grooves of both the core and stopper rings.
It is very difficult and troublesome to apply the adhesive to both the hole surfaces of the stacked webs and the core outer surface, while the stacked webs are provisionally compacted by an appropriate means. Particularly speaking, while the stacked webs are provisionally compacted between the opposite bases with their holes in combination forming a vertically extending hole, the adhesive is poured into the vertical hole from an upper end thereof and concurrently the hollow core with a bullet-like closure or plug temporarily mounted on the upper core end is disposed into the vertical hole from a lower end thereof. These concurrent operations are very troublesome and are likely to cause the stacked webs and the environment around the webs to become dirty with a part of the adhesive discharged from the vertical web hole. According to this conventional method, the provisional compacting operation is obliged to take a long time until the adhesive is cured. Further, the above assembling operation with the separate parts, i.e., the core, the paired ring plates and the paired stopper rings, using the adhesive is also troublesome.
The above first and second methods require thin backing plates of a disk form, each having a central hole coinciding with the web hole. The backing plates are of a rigid paper and have the same diameter as that of the base smaller than that of web (see "150" in FIG. 4). The stacked webs include the backing paper plates, each interposed between neighboring groups of the webs, each group consisting of several webs. The interposed backing plates are adapted to prevent the stacked and compacted webs held by the opposite bases from moving tangentially or rotating relative to each other, by friction exerted between each backing plate and neighboring webs, while the abrading disk tool with the compacted webs is in operation or works with a product to be ground. The backing plates also keep the piled webs compacted together by the same friction over at least radially inner web portions backed by the backing disk plates. This is effective, even if the webs are partially pressed by the product so that the webs would be, otherwise, separated into two groups over the entire radial portions.
The third known method of producing an abrading disk tool with the compacted abrasive webs using an adhesive, was invented by the inventor of the present application. This is a method improved from the above second method using the adhesive in that the troublesome operation for disposing the hollow core into the stacked webs is avoided. This is because there is no core required, and the opposite bases for holding the compacted webs therebetween are no longer required. Further, the before-mentioned backing plates are no longer required. Of course, such backing plates may be interposed in the stacked webs.
Abrading disk tools produced by this improved method are now becoming more widely used. According to the improved method, abrasive non-woven fibrous webs are die-cut, each to have a disk form with a central hole having key grooves for a key projection of a rotation driving spindle or shaft and a plurality of peripheral holes arranged around the central hole. The die-cut disk webs are stacked one on another, and are covered by an upper covering member having holes temporarily applied at a top side of a combination (i.e., brush) of the stacked webs having a vertical axis with the member holes opening to the central and peripheral holes of the web combination. Further, the web combination is covered by a lower covering member temporarily applied to close the central and peripheral holes of the web combination at the bottom side thereof.
The covered web combination is provisionally compacted, and at the compacted state, an adhesive is poured into the holes of the web combination from the top side thereof to fill the holes with the adhesive. The covered compacted web combination with the adhesive is kept for a sufficient time, as it is to have portions of the web combination around the central and peripheral holes impregnated with the adhesive, and then the surplus or non-impregnated parts of the adhesive in the central and peripheral holes are discharged out of the web combination. The covered web combination is kept as it is, while it is compacted, for another time enough to have the impregnated adhesive parts cured completely.
As a result, when the upper and lower covering members are removed, an abrading disk tool with no core and backing plates is completed. Of course, such backing plates may be interposed as in the above second method. The adhesive impregnated portions of the web combination around the respective peripheral holes are rigid due to the cured adhesive, as well as the adhesive impregnated portion around the central hole. Therefore, the rigid portions prevent the stacked webs from moving relative to each other and keep the stacked webs compacted together over non-impregnated web portions radially inwards of the impregnated web portions around the peripheral holes.
The adhesive impregnated web portions around the central hole for the spindle to be held at the key grooves and those around the peripheral holes which may be used for at least a pair of auxiliary shafts, all work effectively as means for holding the stacked webs in a compacted state.
The third method as described above is advantageous over the first and second methods in various aspects, but still encounters a difficult problem wherein use of the adhesive leads to troublesome operations, although the difficulty is reduced relative to that in the second method, and still requires means for provisionally compacting the stacked webs and a long production time mainly taken for curing the adhesive, even if an abrading disk tool with stacked webs small in size and/or the entire thickness is produced. This leads to a low productivity of the tool.
Further, there still remains substantially the same inherent problem as that of the second method; that is, the adhesive handling operation is apt to cause the stacked webs and the environment around the same to be polluted with the adhesive during production of the tool. Such adhesives, particularly solvent-based adhesives are not environmentally favorable, particularly in Europe, and even in this regard it is preferable to avoid use of adhesives in production of abrading brush tools, if possible.